1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which are suitable for a broadcasting television camera, a video camera, a digital still camera, and a silver-halide film camera, for example.
2. Description of the Related Art
As to a conventional so-called four-unit zoom lens for a television camera, there are proposed various structures for achieving wide angle, high magnification, and high performance. For instance, Japanese Patent Application Laid-Open No. 2005-227494 proposes an inner-focus-type zoom lens in which a first lens unit is divided into a negative lens unit G11, a first positive lens unit G12, and a second positive lens unit G13 in order from an object side, and the first positive lens unit G12 is moved on an optical axis for performing focusing.
In addition, in recent years, as to a so-called rear-focus-type zoom lens in which a lens unit other than the first lens unit is used for performing focusing, there is proposed a zoom lens in which a change of a zooming ratio due to a focus distance when focusing is performed by a zoom lens unit is noted (see Japanese Patent Application Laid-Open No. H09-015495 and Japanese Patent Application Laid-Open No. H02-154216).
Japanese Patent Application Laid-Open No. H09-015495 proposes a rear focus type having a structure in which, in a five-unit zoom lens, second to fourth lens units are zoom lens units, the fourth lens unit also works for correction of a change of an imaging position due to focusing, and a movement amount of the second lens unit is changed in accordance with a focusing distance.
Japanese Patent Application Laid-Open No. H02-154216 proposes a rear focus type having a structure in which, in a four-unit zoom lens, a zooming portion is used for focusing, and each zoom lens unit is moved in accordance with focusing so that a zooming ratio is not decreased depending on an object distance.
A zoom lens of Japanese Patent Application Laid-Open No. 2005-227494 is an inner focus type using a first unit having a large lens diameter, so that it is difficult to achieve smaller size and lighter weight of the lens because the number of lenses constituting a focus lens unit is large.
As to the zoom lens of Japanese Patent Application Laid-Open No. H09-015495, in order to achieve a high zooming ratio so as to perform focusing by the zoom lens unit, there is a problem in that it is difficult to achieve smaller size and lighter weight of the lens because it is necessary to secure a large stroke of a second unit.
As to the zoom lens of the Japanese Patent Application Laid-Open No. H02-154216, it is necessary to use multiple lens units required to move for focusing, and it is necessary to secure a drive mechanism and a drive space. Therefore, it is difficult to achieve higher magnification and to achieve smaller size and lighter weight of the lens at the same time.
In the five-unit zoom lens as the present invention in which the second to fourth units are the zooming portion, and the fourth unit also works as the focus lens unit, in order to achieve both higher zooming ratio and suppression of decrease of the zooming ratio in short distance imaging, it is important to appropriately set zoom sharing ratios of the second unit and the third unit with respect to the zooming ratio of the entire lens.
Other than that, it is important for downsizing of the focus lens unit and reduction of a movement amount for focusing to appropriately set a relationship between a focal length of the third unit and a focal length of the fourth unit, and to appropriately set a relationship among lateral magnifications of lens units of the fourth unit and thereafter.